At least 14 people have died in a recent outbreak of Nipah virus in India's southern state of Kerala, according to the World Health Organization (WHO). The virus—which is thought to be the inspiration for the 2011 science fiction movie Contagion—is rare but often deadly.

The outbreak is ongoing in Kerala, and there have been 16 confirmed cases, 12 suspected cases, and 14 deaths, the WHO reports.

Although there has never been a Nipah infection in the U.S., there have been local outbreaks in Malaysia, Bangladesh, and India.

Nipah is considered a zoonotic disease, meaning it’s usually transferred from animals to humans, typically when people come into contact with bodily fluids of animals.

Nipah virus is generally carried by bats (particularly large fruit bats), Stephen Luby, M.D., an infectious disease and geographic medicine professor at Stanford University, tells SELF. It's uncommon to see this type of infection outside of bats, and the virus doesn't make them sick. However, most other mammals experience symptoms if they are infected. In humans, Nipah infections manifest with symptoms including fever, respiratory issues, and severe headaches. The infection can lead to brain damage and death.

For example, people became infected with Nipah virus in Bangladesh in 2004 after drinking date palm sap that was contaminated by infected fruit bats; the bat's saliva got into sap that was tapped from trees, which people then drank, Dr. Luby explains.

However, more than 600 cases of human-to-human transmission were reported between 1998 and 2015, according to the WHO. And the fact that Nipah transmission has occurred between humans in some recent cases is concerning.

“This is another example of an infectious disease outbreak that should put people on notice,” infectious disease expert Amesh A. Adalja, M.D., senior scholar at the Johns Hopkins Center for Health Security, tells SELF. But it's important to point out that Nipah “can’t transmit efficiently” from human to human, Dr. Adalja adds. "This is not contagious in the same sense that the flu is," T. G. Ksiazek, Ph.D., a professor in the departments of pathology, microbiology, and immunology at the University of Texas Medical Branch, tells SELF.

But the fact that it's happening at all is particularly worrying because "most of the devastating infectious diseases in human history began as infections that spilled over from animals and the people and then acquired the capacity for efficient person-to-person transmission," Dr. Luby says—such as HIV, measles, and tuberculosis.

Nipah virus is also worrisome because it can be deadly, and even those who survive the infection may end up dealing with long-term health issues.

After a person is exposed to the Nipah virus, it may take between five and 14 days before they start to experience any symptoms, according to the Centers for Disease Control and Prevention (CDC). Then, the person may have a fever, headache, and/or sometimes a respiratory illness for anywhere from three to 14 days, followed by drowsiness, disorientation, and mental confusion. Symptoms can progress to a coma and lead to encephalitis (inflammation of the brain).

Although there aren't clear stats about how deadly Nipah virus infections are, the CDC notes that during a Nipah virus outbreak between 1998 and 1999, about 40 percent of people who went to the hospital for Nipah infections died.

“This is a terribly serious disease,” William Schaffner, M.D., an infectious disease specialist and professor at the Vanderbilt University School of Medicine, tells SELF. “Even people who survive it can have a long-term disability. It’s a really nasty infection.” Persistent convulsions and personality changes have happened to some people, the CDC says, and some patients have experienced a reactivation of the virus months and even years after they were exposed.

There is also no known cure: "Once people become infected and symptomatic, there is no proven effective therapy," Dr. Luby says. So the only treatment available is supportive care, including things like IV fluids to prevent dehydration and anti-seizure medication, Dr. Adalja says.

Nipah is rare, but infectious disease experts are keeping an eye on it.

The WHO added Nipah virus to its list of “priority diseases” earlier this year, along with more well-known conditions like Ebola, Zika, and SARS.

However, there has never been a Nipah infection in the U.S., or even in this hemisphere, Dr. Schaffner notes. So the major risk right now is to people in the Kerala area in India or those who are traveling there. If you're traveling in the area, it's a good idea to steer clear of date palm sap, which has been linked to Nipah virus in the past, but you should otherwise be OK, Ksiazek says.

Ultimately, “this is not something the average American needs to worry about,” Dr. Adalja says.